1. Field of the Invention
The present invention relates to an alloy for a soft magnetic layer in a perpendicular magnetic recording medium excellent in saturation magnetic flux density, amorphousness, and atmospheric corrosion resistance.
2. Description of the Related Art
In recent years, accompanied with remarkable progress of magnetic recording technology, recording density of the magnetic recording medium is becoming higher to increase the capacity of the drive. However, for the magnetic recording medium with a longitudinal magnetic recording system that is widely used currently, since the recording bit must be miniaturized in order to realize the high recording density, high coercivity is required such that the recording with the recording bit is not possible. Therefore, a perpendicular magnetic recording system is being investigated as a means to solve these problems and increase the recording density.
In the perpendicular magnetic recording system, the axis of easy magnetization is formed to be oriented perpendicular to the medium surface in the magnetic film of the perpendicular magnetic recording medium and this system is suitable for high recording density. In this perpendicular magnetic recording system, a double-layer recording medium having a magnetic recording layer with high recording sensitivity and a soft magnetic layer has been developed. For this magnetic recording layer, a CoCrPt—SiO2-based alloy is commonly used.
On the other hand, as the soft magnetic layer, a CoZrNb/Ta alloy disclosed in, e.g., Japanese Patent Laid-Open Publication No. 2005-320627, an (Fe, Co, Ni) (Al, Cr) (B, Nb, Zr, Ta, Hf, Ti, V) alloy disclosed in, e.g., Japanese Patent Laid-Open Publication No. 2007-284741, and the like have been proposed.
However, the CoZrNb/Ta alloy described in Japanese Patent Laid-Open Publication No. 2005-320627 provides only a lower level of saturation magnetic flux density compared to that required for the soft magnetic layer of the perpendicular magnetic recording medium. In contrast, an alloy with a high saturation magnetic flux density has been developed as disclosed in Japanese Patent Laid-Open Publication No. 2007-284741. The saturation magnetic flux density of this alloy has been increased by the addition of Fe, while preventing deterioration of atmospheric corrosion resistance as its adverse effect by the addition of Al/Cr. This alloy has excellent saturation magnetic flux density and atmospheric corrosion resistance as the soft magnetic film in the perpendicular magnetic recording medium. However, performances required for the soft magnetic film in the perpendicular magnetic recording medium is recently becoming so high that even the alloy described in Japanese Patent Laid-Open Publication No. 2007-284741 cannot fully satisfy the required performances. As used herein, atmospheric corrosion resistance means corrosion resistance in indoor environments where an apparatus equipped with an electronic component(s) is used. In addition, amorphousness means easiness of amorphous formation when the alloy is quenched and solidified or sputtered for film forming.